1. Field of the Invention
The present invention relates to branch pipes for rail car braking system and, more particularly, to a branch pipe having an integral volume that increases the effective length of the brake pipe of a rail car.
2. Description of the Related Art
The AAR standards define brake performance requirements for standard length cars with a brake pipe length in the range of 45 feet to 75 feet, and long cars with brake pipe length of more than 75 feet to 110 feet. The AAR compliant brake control valves are tuned to provide AAR specified brake performance, including emergency sensitivity, for the brake pipe volume corresponding to these brake pipe lengths.
Iron ore cars, and other cars carrying very heavy loads, are often much shorter than the AAR standard car lengths so that they meet the axle load limits of 31 tons due to the density of the iron ore or other material. For this reason, iron ore cars may have brake pipe lengths shorter than 35 feet. If a standard AAR control valve is applied to a car with this reduced brake pipe volume, emergency sensitivity, quick service, and other control valve functions which are proportional to the brake pipe volume may be adversely impacted. The adverse impacts can include the potential for undesired emergency brake applications, which can have a significant impact on train operations and safety.
Several remedies are well known, but have disadvantages that remain unaddressed in the art. De-tuned control valves, known as SS for “super short” valves, have been offered for short cars. SS valves generally have a desensitized Emergency Portion, but heretofore have not addressed the quick service and other brake pipe volume dependent functions of the Service Portion. Significantly, SS valves are not defined by an AAR standard, and are generally not poke yoked to prevent misapplication of a standard valve. AAR standards require a longer mounting stud on the pipe bracket for “long” valves to prevent misapplication of long/standard valves. Because the SS valve is not made to any AAR standard, this provision is not addressed. As a result, SS valves have generally been applied only to closed, non-interchange railway operations, where there is no opportunity to mix up control equipment on the car during maintenance.
It is also known to address the issue of reduced brake pipe volume on short cars by the addition of a volume or by using larger-diameter, non-AAR standard pipe for the brake pipe. While both solutions provide acceptable technical solutions, they are generally resisted by the car builders, as both require additional engineering and add cost to the car. Both solutions require additional pipe fittings, first to tee off the brake pipe and pipe to a standalone volume, and second for the expansion and reducing of pipe fittings as needed to adapt a larger brake segment to the AAR standard (1¼ IP) pipe fittings.